The present invention relates to the bearing structure of a motor in which a shaft is supported by an oil retaining bearing.
A motor that has an oil retaining bearing is widely used as a small motor in audio-visual equipment. In place of a ball bearing, an oil retaining bearing is used to support a shaft of such a small motor promoting greater cost-effectiveness. The oil retaining bearing is disposed around a shaft in a pocket of a casing of a motor as disclosed in U.S. Pat. No. 5,899,572.
However, in the known bearing structure of a motor as above, it is disadvantageous for the oil retaining bearing in the pocket of the casing to loosen owing to vibration caused by rotation of the motor and external force on the shaft. The oil retaining bearing as loosened is likely to come out of the pocket or to rotate together with the shaft in the pocket.
The oil retaining bearing is strongly engaged in the pocket. If they are caulked together, the oil retaining bearing is deformed thereby making insertion of the shaft more difficult and hindering the maintenance of a predetermined clearance to affect its rotation.
When external force is applied to the shaft of the motor in a thrust direction, the shaft is moved in the same direction by the external force. Thus, a commutator or a gear engaged in the shaft of the motor is moved together in the thrust direction. Owing to such motion in the thrust direction, the commutator and gear are deviated from a normal position to affect operation of the gear thereby causing noise. It is difficult to obtain the same play in the thrust direction in a known ball bearing of a motor.
If the commutator is deviated from a normal position, relative position to a magnet in the casing will lead abnormal rotation. Furthermore, if the gear and commutator are deviated widely in the thrust direction, they are engaged with the oil retaining bearing causing mechanical abnormality at the engagement position resulting in abnormal rotation.
Therefore, in the known bearing structure having an oil retaining bearing, it is difficult to restrain the motion of a shaft of a motor in the thrust direction.